The 3rd Generation Partnership Project (3GPP), which is a standardization project, standardized the Evolved Universal Terrestrial Radio Access (hereinafter referred to as E-UTRA), in which high-speed communication is realized by adopting an Orthogonal Frequency-Division Multiplexing (OFDM) communication scheme and flexible scheduling using a unit of prescribed frequency and time called Resource Block.
Moreover, the 3GPP discusses Advanced E-UTRA, which realizes higher-speed data transmission and has upper compatibility with E-UTRA. E-UTRA relates to a communication system based on a network in which base station devices have substantially the same cell configuration (cell size); however, regarding Advanced E-UTRA, discussion is made on a communication system based on a network (different-type radio network, Heterogeneous Network) in which base station devices (cells) having different configurations coexist in the same area. Note that E-UTRA is also referred to as Long Term Evolution (LTE) and Advanced E-UTRA is also referred to as LTE-Advanced. Furthermore, LTE can also be used as collective term including LTE-Advanced.
Specification is made on a carrier aggregation (CA) technique and a dual connectivity technique, in which, in a communication system where cells (macro cells) having large cell radii and cells (small cells) having smaller cell radii than those of the macro cells coexist as in a Heterogeneous Network, a terminal device performs communication by connecting to a macro cell and a small cell at the same time (NPL 1).
Meanwhile, in NPL 2, Licensed-Assisted Access (LAA) is discussed. In LAA, for example, an Unlicensed spectrum used by wireless Local Area Network (LAN) is used as LTE. Specifically, the Unlicensed spectrum is configured as a Secondary cell (secondary component carrier). A Secondary cell used as LAA is assisted regarding connection, communication, and/or configuration by a Primary cell (primary component carrier) configured in a Licensed spectrum. As a frequency band available in LTE is expanded by LAA, broadband transmission becomes possible. Note that LAA is also used in a shared spectrum shared among prescribed operators.
Furthermore, in a system aiming at safe and secure communication, latency in radio communication is one of important issues. In LTE including LTE using LAA as well as LTE using a Licensed spectrum of the related art, it is also important to further reduce such latency.
Moreover, a terminal device performs measurement of RSRP, RSRQ, and the like, based on a Reference Signal (a CRS, CSI-RS, DS, and the like) transmitted from a base station. Then, a Reference Signal may be transmitted based on downlink LBT in an LAA cell. That is, in an LAA cell, even in a time/frequency in which a Reference Signal is assumed to be transmitted in a terminal device, in a case that a channel is busy based on downlink LBT, the Reference Signal may not be actually transmitted.